Determining the age of an object from the → radioactive decay
of its constituting material. The technique consists of comparing the
→ abundance
ratio of a → radioactive isotope to its
→ decay product. This will yield the number of
half-lives that have occurred since the
sample was formed. More specifically, if an object is made up of 50 % decay product
then it has gone through 1 → half-life.
75% decay product equals 2 half-lives, 87.5% decay product equals 3 half-lives,
93.76% decay product equals 4 half-lives, and so on. For example,
the decay product of → uranium-238 (238U) is
→ lead-206 (206Pb).
The half-life of 238U is 4.5 billion years. Hence, if the sample has gone
through two half-lives, it is 9 billion years old.
See also: → radiocarbon dating.